1. Field of the Invention
The present invention is related to a multiplexer of an encoded video, and particularly to a multiplexer of an encoded video which enables the video of moving pictures of a plurality of channels to be encoded and transmitted at once in cable television broadcasting stations, video libraries or the like.
2. Description of the Prior Art
In the conventional video encoder system, there is a technique in which no bit rate control of the total system is performed, and a technique in which the bit rate control is performed by switching a plurality of previously prepared quantizers.
In the former technique, as shown in FIG. 14, each of N encoders E1 to EN is fixed to a bit rate A, and the encoding is performed at the bit rate A whether the amount of information contained in the picture input to the encoders E1 to EN is large or small.
In the latter technique, as shown in FIG. 15, a plurality of quantizers of different bit rates are provided in each encoder E1 to EN, and by determining the amount of information contained in the picture input to each encoder with an information amount estimation unit 41, the quantizer of each encoder is selected. For instance, if the amount of information contained in the picture input to the encoder E1 is small, the quantizer X having a bit rate A/2 is selected. If the picture information input to the encoder E2 has a moderate amount of information, the quantizer Y having a bit rate A is selected. Further, if the amount of information contained in the picture input to the encoder EN is large, the quantizer Z having a bit rate 3 A/2 is selected. In addition, the total bit rate to be output from an adder 40 is made to be N.A.
However, the above prior art has the following problems. In accordance with the technique shown in FIG. 14, the encoders E1 to EN perform the encoding at the same bit rate whether the amount of information contained in the picture input to them is large or small. For this, extreme deterioration occurs in pictures containing a large amount of information, or conversely, insufficient amount of information corresponding to a predetermined bit sate is generated in pictures Containing a small amount of information and dummy bits need to be added. As a result, it cannot be said that transmitted information is completely effectively utilized, and there is a problem that the subjective evaluation of the total system drops because of extremely deteriorating pictures.
In addition, in accordance with the technique shown in FIG. 15, in the encoders E1 to EN, only a finite number of types of quantizers X to Z can be prepared. For this, the bit rate of the encoders cannot be set to a value corresponding to the amount of information of the input picture, and thus there is a problem that effective utilization of the transmitted information is not sufficient though improved as compared with the technique of FIG. 14. It is necessary to increase the number of the quantizers to be provided, but there are many problems in putting this to practical use.